A gas turbine engine 210 is shown in schematic section in FIG. 1 and comprises a main rotational axis 208, an air intake 212 and a propulsive fan 214 that generates two airflows A and B. The gas turbine engine 210 comprises, in axial flow A, an intermediate pressure compressor 216, a high pressure compressor 218, a combustor 220, a high pressure turbine 222, an intermediate pressure turbine 224, a low pressure turbine 226 and an exhaust nozzle 228. A nacelle 230 surrounds the gas turbine engine 210 and defines, in axial flow B, a bypass duct 232 between the air intake 212 and an exhaust nozzle 234. A rear engine mounting arrangement 22 (rear in the sense of airflows A and B) is shown in the vicinity of the turbines 222, 224, 226. Thrust struts 26 connect the rear engine mounting arrangement 22 with a forward section of the engine 210. The rear engine mounting arrangement 22 is connectable to an aircraft pylon 206 and is located at a radially outer extent of the engine 210, Preferably, at top dead centre. For the purposes of the following description, this will be taken to be vertically above the engine although it should be understood that the engine 210 may be hung at an angle to the vertical.
An engine 210 is conventionally mounted on an aircraft, whether under a wing or against a fuselage by each of a front and a rear mounting arrangement. Where the engine is a gas turbine engine 210, the front mounting is generally provided in the vicinity of the fan 214 or compressors 216, 218 and the rear mounting is generally provided in the vicinity of the turbines 222, 224, 226. However, other arrangements are possible. The rear mounting arrangement 22 comprises means for connection of thrust struts 26 to transfer the thrust generated by the engine 210 through the mounting arrangement 22 and the pylon 206 to the aircraft. The rear engine mounting arrangement 22 also comprises means to transfer vertical and side loads from the engine 210 through the pylon 206 to the aircraft. Typically a forward engine mounting arrangement (not shown) is also provided. Preferably, in the vicinity of the compressors of a gas turbine engine 210 to transfer engine side and vertical loads but not thrust loads.
A conventional rear engine mounting arrangement 22 is shown in FIG. 2 in highly schematic form. The arrangement comprises a mount block 10 that includes means to attach it to the aircraft pylon 206 and two engine attachment links 24 for connection to the engine 210. It further comprises an integral clevis arrangement 12 protruding forward from the main body of the mount block 10. The clevis arrangement 12 has a main thrust connection 14, which is connectable to a thrust yoke 16 by a pivot pin or similar, and a pair of catcher devises 20 located on either side of the main thrust connection 14 that define a clearance around their respective pins. The yoke 16 is connected to the thrust struts 26 (FIG. 1) at connection points 18 by pin and clevis arrangements. Thus the propulsive thrust loads are transferred from the engine 210 through the thrust struts 26, yoke 16, main thrust connection 14 and mount block 10 and from there into the pylon 206 of the aircraft. In the event of a failure of the main thrust connection 14, the clearance in the catcher devises 20 is taken up and the thrust load transferred through these instead.
Conventionally, the two integral engine attachment legs 24 are provided at the lateral ends of the mount block 10. An integral catcher leg may also be provided intermediate the engine attachment legs 24 which transfers engine loads in the event of failure of one or both of the engine attachment legs 24. One disadvantage of this engine mounting arrangement is that a failure crack emanating from either of the engine attachment legs 24, or the mount block 10 itself, can propagate through the mount block 10 to fail the adjacent catcher link without detection. Whilst this can be certified by crack growth and propagation analysis, this is an unsatisfactory solution since it requires heavier and stronger materials to ensure the minimal crack growth properties required. This is the case even with more complex arrangements of engine attachment legs 24 and catcher links described in the prior art.
Thus, it is desirable to have an engine mounting arrangement that has a failure load path that does not rely on crack growth and propagation analysis. The present invention seeks to provide a novel rear engine mounting arrangement that seeks to address the aforementioned problems.